Submission #340169

#	Time	Username	Problem	Language	Result	Execution time	Memory
340169		blue	Boat (APIO16_boat)	C++11	9 / 100	14 ms	388 KiB

boat

#include <iostream>
#include <algorithm>
using namespace std;

/*
dp[i][j] = number of valid configurations for schools 1..i but such that i has range a[j] to b[i]

Let us malong longain a long range partitioned by polong longs P[i]
Each section of the range looks like:
A[p] to A[q]-1;
A[p] to B[q]
B[p]+1 to A[q]-1;
B[p]+1 to B[q]
*/

long long mod = 1e9 + 7;

long long a[501], b[501];

long long pos(long long i) //upper acceptable limit of range
{
    if(i > 0) return a[i] - 1;
    else return b[-i];
}

int main()
{
    long long N;
    cin >> N;
    for(long long i = 1; i <= N; i++) cin >> a[i] >> b[i];

    long long I[2*N];
    for(long long i = 0; i < N; i++)
    {
        I[i] = i+1;
        I[i+N] = -i-1;
    }

    sort(I, I+2*N, [] (long long x, long long y)
    {
        return pos(x) < pos(y);
    });

    long long dp[2*N]; //number of streams in between I[i-1] and I[i].
    for(long long i = 0; i < 2*N; i++) dp[i] = 0;

    long long temp = 0;
    long long temp2;
    long long temp_dp;
    for(long long i = 1; i <= N; i++)
    {
         // cout << "i = " << i << '\n';
        temp = 0;
        for(long long j = 1; j < 2*N; j++)
        {
            temp_dp = dp[j];
            int S = pos(I[j]) - pos(I[j-1]);

            if(pos(I[j]) <= pos(i)) temp = (temp + dp[j]) % mod;
            else if(pos(I[j]) <= pos(-i))
            {
                temp2 = temp;
                temp = (temp + dp[j]) % mod;
                if(j > 0) dp[j] = (dp[j]   +   S*temp2  ) % mod;
            }
            int Ssum = (((S-1)*S)/2) % mod;
            dp[j] = (dp[j] + (temp_dp * Ssum) % mod) % mod;
        }
        for(int j = 1; j < 2*N; j++)
        {
            if(pos(i) < pos(I[j]) && pos(I[j]) <= pos(-i))
            {
                dp[j] = (dp[j] + pos(I[j]) - pos(I[j-1])) % mod;
            }
        }
        // for(long long j = 0; j < 2*N; j++)
        // {
        //     cout << j << ' ' << I[j] << ' ' << pos(I[j]) << ' ' << dp[j] << '\n';
        // }
        // cout << "_________________________\n";
    }
    long long res = 0;
    for(long long j = 0; j < 2*N; j++) res = (res + dp[j]) % mod;

    cout << res << '\n';
}

• Subtask 1: 9 / 9
• Subtask 2: 0 / 22
• Subtask 3: 0 / 27
• Subtask 4: 0 / 42